As you see from the slides you cited, it takes a little work to use JSF with portlet modes. After that talk, I came up with a slightly different approach shown here: http://wiki.apache.org/myfaces/UsingPortletModes
Some others have tried it out and improved upon it.
JSR-301 promises to standardize a way to use modes with JSF portlets, but that is a long way off. For now, the best way to accomplish the mode changes will be application dependent. Because the mode changes are done before the JSF lifecycle methods are called, it really doesn't have much to do with Seam. So Seam shouldn't enter into the mix here.
Ok thanks. I will try it out.